The present invention relates generally to valve position systems, and more particularly, to a flexure used in a current-to-pneumatic (I/P) converter, a low cost I/P converter, and a dynamically balanced pneumatic amplifier.
One major purpose of an I/P converter is to produce a pneumatic pressure proportional to a given electrical current. This produced pressure may be referred to as a signal pressure. This signal pressure is traditionally amplified, both in pressure and volume, and fed to a pneumatic actuator used to position a valve in a valve positioner system as described in the U.S. patent application Ser. No. 09/118,406, which is assigned to the same assignee and incorporated herein by reference.
In addition, in a typical 2-stage valve positioner, the second stage is used to amplify both the flow capacity and pressure range of the output since a typical I/P converter has a low flow and minimal pressure gain. Masoneilan and other pneumatic control valve positioner manufacturers have traditionally used two types of pneumatic amplifiers. One type is a spool valve design. The second type is of a pneumatic relay, which is commonly called a relay. The spool valve provides a very consistent dynamic response, but is difficult to manufacture to ensure that it performs well in a steady state. The traditional relay type is easy to manufacture and has a good steady state performance, but lacks in its ability to perform with a consistent dynamic response. Inherent to the design of the relay is an end loading of a supply plug on a corresponding supply seat during steady state operation of the relay. This end loading is due to the pressure drop across the plug and the force due to a supply plug spring. During a dynamic response of the relay, a signal pressure must be increased sufficiently to overcome this end loading before any additional output flow is established. This change in signal pressure with no corresponding output flow is referred to as a flow deadband.
For the improvement of the valve positioner system, what is needed is a low cost I/P converter for use in an electro-pneumatic positioner which operates with supply pressures between 20 psi and 100 psi.
What is also needed is a flexure used in the I/P converter for use in the electro-pneumatic positioner. The characteristics of this flexure must provide temperature and vibration resistance for the I/P converter. Also this flexure should be capable of providing sufficient gain required for operating the electro-pneumatic positioner.
What is further needed is an improved design of the relay type amplifier, which provides consistent dynamic response with minimal effect on the manufacturability or its steady state performance.